Portable grinder with double seal bearing

ABSTRACT

The invention is based on a power tool ( 10 ), in particular a power sander ( 101, 102, 103 ) with a housing ( 12, 112, 212 ) and a motor ( 20, 120, 220 ), supported in the housing, that has a rotatable drive shaft ( 22, 122, 222 ) which is connected operatively by one end to a tool ( 50, 150 ), and in particular carries a sanding plate that can be equipped with grinding means ( 52 ), relative to which sanding plate the drive shaft ( 22, 122, 222 ) is rotatably supported by means of a bearing ( 25, 125, 425 ), in particular by means of a roller bearing with an inner race ( 28 ) and outer race ( 30 ) spaced apart by a bearing gap ( 26 ) and with rotationally fixed and rotatably disposed parts, and in particular is provided with means for removing grinding dust. 
     It is proposed that a bearing ( 425 ) closely adjacent to any incident grinding dust and/or chips created has, on at least one side of its bearing gap ( 26 ), a plurality of sealing disks ( 38, 40 ), in particular two of them, disposed side by side.

PRIOR ART

The invention is based on a power tool, in particular a power sander, asgenerically defined by the preamble to claim 1.

In eccentric sanders and orbital sanders, it is known to usetwo—paired—ball bearings in line with one another to transmit a rotarymotion or to generate an oscillating motion from a drive unit to asanding plate.

This ball bearing, because of the structural design of such products, isalways surrounded by abraded grinding material created during the work.This can happen because of air mixed with grinding material, or fromturbulence in the region of the ball bearing.

Rotating masses create moments that twist an inner race and an outerrace of the ball bearing counter to one another, so that a ball bearingseal between the inner race and the outer race lifts up and no longerperforms its function. This creates a gap, which can allow grindingmaterial to reach the interior of the ball bearing, and bearinglubricant can escape.

The invasion of grinding material and/or the escape of bearing lubricantbetween the ball bearing seal and the inner race or outer race of theball bearing can lead to the destruction of the ball bearing and afailure of the eccentric sander or orbital sander. The resultant damagecan be corrected only with what is usually an expensive repair.

Typically, to prevent tool failure, the intent is to prevent grindingmaterial from being able to enter and mix with the bearing lubricant,which is accomplished by additionally using sealing disks, spin disks,and/or sealing rings.

ADVANTAGES OF THE INVENTION

The invention is based on a power tool, in particular a power sanderwith a housing and a motor, supported in the housing, that has arotatable drive shaft which is connected operatively by one end to atool, and in particular carries a sanding plate that can be equippedwith grinding means, relative to which sanding plate the drive shaft isrotatably supported by means of a bearing, in particular by means of aroller bearing with an inner race and outer race spaced apart by abearing gap and with rotationally fixed and rotatably disposed parts,and in particular is provided with means for removing grinding dust.

It is proposed that a bearing closely adjacent to any incident grindingdust and/or chips created has, on at least one side of its bearing gap,a plurality of sealing disks, in particular two of them, disposed sideby side.

Instead of the single sealing disk that is usual at present, preferablyat least two sealing disks per side are built into the bearing,preferably a roller bearing, with one sealing disk succeeding the otherin the sealing gap. As a result of the sealing disks, a kind oflabyrinth system can be achieved, and it can be reliably prevented thatforeign substances will penetrate the bearing and/or that lubricantswill escape. The positioning of the sealing disks can be done inside acomponent, in particular inside the outer race of a ball bearing. Bymeans of the sealing disks, a sealing system can be achieved that is farmore effective than a single sealing disk or than the combination ofsuch a sealing disk with an additional seal. An undesired leakage gapfrom twisting of the outer race and inner race of the ball bearingrelative to one another can be reliably prevented because of theattainable labyrinth effect. An advantageous labyrinth effect and aspace-saving construction can be achieved in particular by means ofclosely adjacent sealing disks that preferably brace one anotheraxially.

To minimize friction, toward the outside one grinding sealing disk andfollowing it a contactless sealing disk can be used. With a contactlesssealing disk in the axially inner region, it can also be achieved thatlubricant that has penetrated between the sealing disks can flow backagain. In principle, however, two or more grinding sealing disks or twoor more contactless or non-grinding sealing disks each are alsoconceivable.

The proposed sealing system requires no further structural space outsidethe ball bearing, and an additional clamping of seals outside thebearing, and friction caused by an additional seal, can be avoided. Bythe use of the ball bearing with integrated sealing disks located oneinside the other, only one component is required. Additional sealsbefore and after the ball bearing can be avoided; the effort of assemblycan be simplified; and additional errors from incorrect installation canbe prevented. Furthermore, the sealing system is especially low in wear,since the sealing disks are encapsulated by the inner and outer racesand are protected against external influences.

In order to achieve sealing disks that are advantageously as stiff aspossible across the bearing gap, these sealing disks at least in parthave a concave contour and/or have an inner metal part forreinforcement, preferably a zinc-coated sheet-metal part.

It is also proposed that the degree of filling of the bearing withlubricant is between 40% and 50%, and as a result a large reserve volumeand a long service life can be attained.

DRAWING

Further advantages will become apparent from the ensuing description ofthe drawing. In the drawing, exemplary embodiments of the invention areshown. The drawing, description and claims include numerouscharacteristics in combination. One skilled in the art will expedientlyconsider the characteristics individually as well and put them togetherto make useful further combinations.

Shown are:

FIG. 1, an orbital sander in longitudinal section;

FIG. 2, an eccentric sander in longitudinal section;

FIG. 3, a detail of a right angle grinder in longitudinal section;

FIG. 4, a detail of an orbital sander of FIG. 1, with a multiplysealed-off eccentric bearing on both outer sides;

FIG. 5, a detail of an eccentric sander of FIG. 2, with a multiplysealed-off eccentric bearing on both outer sides as in FIG. 4;

FIG. 6, an eccentric bearing designed as a two-row angular ball bearing;and

FIG. 7, an enlarged detail 7 of FIG. 6.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a power tool 10, which is designed as a conventionalorbital sander 101 and has a housing 12 with a hand grip 14 and anauxiliary hand grip 16. The hand grip 14 has a toggle switch 18, whichturns the current supply to a motor 20 on and off. The motor 20 has adrive shaft 22, which is rotatably supported on its upper and lower endin a respective bearing 241, 242.

On its lower free end, the drive shaft 22 furthermore has a threadedportion 221, on which an eccentric sleeve 23 is held in a manner fixedagainst relative rotation by means of a nut 29. The eccentric sleeve 23is embraced on the outside by the inner race 28 of an eccentric bearing25, which is seated with its outer race 30 in a manner fixed againstrelative rotation in the bearing eye 502 of a sanding pad holder 501.The sanding pad holder carries a sanding pad 503 and with it forms asanding plate 50.

The sanding plate 50 has continuous suction holes 544, through which—onpassing through the congruent suction holes of a sanding sheet 52fastened to the sole plate of the sanding plate 50—grinding dust createdduring grinding is aspirated or blown out by means of a ventilator 541,which rotates jointly with the drive shaft 22, by way of an extractionconduit to the extractor muff 542 and from there reaches a dustcollection container, not shown.

The sanding sheet 52 is firmly retained on the sanding plate 50 by meansof a chucking cam 56.

Upon rotation of the drive shaft 22, after actuation of the toggleswitch 18, an orbiting motion without independent rotation is impartedto the sanding plate 50; that is, because the drive shaft 22 is capableof rotating freely relative to the sanding plate 50, only the eccentricmotion is imparted to the sanding plate via the eccentric sleeve 23.

Because grinding dust flowing through is so nearby, the conventionaleccentric bearing 25 is protected on its side toward the ventilator 541against the entry of dust and dirt from the outside by separate sealingmeans 32 on the order of shaft seals. This protection is in need ofimprovement.

FIG. 2 shows a conventional eccentric sander 102 with a housing 112 anda hand grip 114 and an auxiliary hand grip 16. Components that remainessentially the same are identified throughout by the same referencenumerals. The hand grip 114 has a toggle switch 118, which turns thecurrent supply to a motor 120 on and off. The motor 120 has a driveshaft 122, which is rotatably supported on its upper and lower end, eachin a respective bearing 241, 242.

Furthermore, on its lower, free end, the drive shaft 122 has a threadedportion 221, with which, on the upper face end of a ventilator 541, itengages the female-threaded portion 129 of the ventilator and receivesthis portion in a manner fixed against relative rotation.

The ventilator 541, on its underside, has an eccentric bore 123, inwhich the outer race 130 of a conventional eccentric bearing 125,designed as a two-row angular ball bearing, is seated in a manner fixedagainst relative rotation. With its inner race 128, the eccentricbearing embraces an eccentric peg 131, which as a result is rotatablysupported relative to the fan 541. By means of a screw bolt 132, a roundsanding plate 150 is fastened in a manner fixed against relativerotation to the free end of the eccentric peg 131.

The sanding plate 150 has a plurality of continuous suction holes 544,through which—after passing through the congruent suction holes of asanding sheet 52 secured to the sole plate of the sanding plate150—grinding dust, conveyed by the ventilator 541 that rotates jointlywith the drive shaft 22, is aspirated or blown via an extraction conduitto the extractor muff 542 and from there reaches a dust collectioncontainer, not shown.

The sanding sheet 52 is firmly held on the sanding plate 50 by means ofa Velcro™ closure.

Upon rotation of the drive shaft 22 after actuation of the toggle switch18, an orbiting motion with simultaneous or superimposed independentrotation is imparted to the sanding plate 50.

On its side toward the ventilator 541, to prevent contact with grindingdust, the conventional eccentric bearing 125 is protected against theentry of dust and dirt by separate sealing means, on the order of shaftseals, not shown in detail. This protection is in need of improvement.

FIG. 3 shows a power tool 10 which is designed as a conventional rightangle grinder 103 and has an elongated housing 212 that acts as a handgrip. It has a toggle switch, not shown, which turns the supply ofcurrent to a motor 220 on and off. The motor 220 has a motor shaft 222,which is rotatably supported on both ends, each in a respective bearing,of which only the front bearing 241 is shown.

The motor shaft 222, on its front end, has a small cone pinion 60, whichis secured with a nut 62 and meshes with a plate wheel 64 and thus formsan angular gear 66. The plate wheel in a manner fixed against relativerotation embraces a work spindle 68, which is supported at the top in aneedle bearing 72 and at the bottom in a flange bearing 72. The flangebearing is seated with its outer race 230 in a manner fixed againstrelative rotation in a bearing flange 74, which can be secured withscrews 76 to the housing 212.

A grinding disk can be secured to the free end of the work spindle 68.

After actuation of the toggle switch, the work spindle 68 rotates, andwith a grinding disk fastened to it, grinding work can be done, whichtypically produces a considerable amount of dust.

To avoid contact with grinding dust, the conventional flange bearing 72is protected on the outside, on both of its outer sides, against theentry of dust and dirt by separate, caplike sealing means 232. Given thestringent demands made in professional use at construction sites, thisprotection is in need of improvement. In a right angle grinder, notshown, the flange bearing is therefore provided on both sides with adual assembly of sealing disks, as shown in FIGS. 6 and 7.

FIG. 4 shows a detail of the orbital sander of FIG. 1, with the detailsdescribed above which will not be repeated here; instead of aconventional eccentric bearing, however, an eccentric bearing 425 thatis multiply sealed off on both outer sides is provided. As a result, theseparate sealing means on the order of shaft seals of FIG. 1 can bedispensed with. The eccentric bearing 425 is protected considerably moresecurely against the invasion of dust and the escape of lubricant thanthe previously used bearing of FIG. 1, and installation is simplerbecause no separate sealing means have to be installed. Furthermore,there is no longer a need to procure the separate sealing means and keepthem in stock.

Instead, the outer race 30, seated in a manner fixed against relativerotation in the bearing eye 502 of the sanding pad holder 501, has twoparallel inner race grooves 36 on each outer side (FIGS. 6 and 7). Onenon-grinding sealing disk and one grinding sealing disk 38, 40,respectively, are each retained by the outer edge 34 in sealed fashionin the respective grooves. The inner edge 35 of each sealing disk 38,40, with its foot region 47, 49, embraces the inner race 28 of theeccentric bearing 425 either in a grinding manner or at a slight gapspacing and forms a labyrinth seal, or the sealing disks 38, 40 form alabyrinth system.

The sealing disks 38, 40 comprise an inner metal part 44, which isspray-coated with plastic (FIGS. 6 and 7).

FIG. 5 shows a detail of the eccentric sander of FIG. 2 with the detailsrecited above, which will not be repeated; instead of a conventionaleccentric bearing, an eccentric bearing 425—as in FIG. 4—that ismultiply sealed off is provided on both outer sides. As a result, theprevious sealing means of FIG. 2 can be dispensed with.

The eccentric bearing 425 is protected considerably more securelyagainst the entry of dust and the escape of lubricant than thepreviously used bearing of FIG. 2, and installation is simpler becauseno separate sealing means have to be installed. Furthermore, it is nolonger necessary to procure the separate sealing means and keep them instock.

Instead, the outer race 30 seated in a manner fixed against relativerotation in the ventilator 541, on each other side, has two parallelinner race grooves 36 (FIGS. 6 and 7). In each of the grooves, onenongrinding sealing disk and one grinding sealing disk 38, 40 each isretained, by the outer edge 34, in sealed fashion. The inner edge 35 ofeach sealing disk 38, 40, with its foot region 47, 49, embraces theinner race 28 of the eccentric bearing 425 in liplike fashion, either ina grinding manner or at a slight gap spacing and forms a labyrinth seal.The sealing disks 38, 40 comprising inner metal part 44, in particularzinc-coated steel, which is spray-coated with plastic.

FIG. 6, in an enlarged view, shows the eccentric bearing 425, designedas a two-row angular ball bearing, each with two sealing disks 38, 40,which seal off the bearing gap 26 on both sides, in a grinding manner onthe outside and a nongrinding manner on the inside.

The inner race 28 and outer race 30 are each wider than in conventionalangular ball bearings, and as a result they can effectively supporttwice the arrangement of sealing rings. The two rows of balls 31 areenclosed or guided by a bearing cage 45.

The sealing disks 38, 40, toward the balls 31, form a platelike hollowprofile, and opposite the inner race 28 with their foot regions 47, 49they form a grinding seal and a narrow-gapped labyrinth seal,respectively.

The eccentric bearing 425 is filled with lubricant 48 to a fillingdegree of 35% to 50%, compared to the filling degree of conventionalbearings, which is 35%, plus or minus a 5% tolerance.

FIG. 7 illustrates the design of the outer race 30 of the bearing 425with two closely adjacent inner race grooves 36, which are disposed insuch a way that the sealing disks 38, 40 rest axially on one another.

The design of the foot regions 47, 49 of the sealing disks 38, 40 isalso clearly visible.

In addition to the exemplary embodiments described, the embodimentaccording to the invention can also be employed in other power toolsthat appear appropriate to one skilled in the art.

List of Reference Numerals

10 Power tool

12 Housing

14 Hand grip

16 Auxiliary hand grip

18 Toggle switch

20 Motor

22 Drive shaft

23 Eccentric sleeve

25 Eccentric bearing

26 Bearing gap of 25, 125, 425

28 Inner race of 25, 125, 425

29 Nut

30 Outer race of 25, 125, 425

31 Balls

32 Sealing means

34 Outer edge

35 Inner edge

36 Two parallel radial grooves

38 Non-grinding sealing disk

40 Grinding sealing disk

44 Inner metal part

45 Bearing cage

47 Foot region

48 Lubricant

49 Foot region

50 Tool, sanding plate

52 Abrasive

56 Chucking cam

60 Cone pinion

62 Nut

64 Plate wheel

66 Angular gear

68 Work spindle

70 Needle bearing

72 Flange bearing

74 Bearing flange

76 Screw

101 Orbital sander

102 Eccentric sander

103 Right angle grinder

112 Housing

114 Hand grip

118 Toggle switch

120 Motor

122 Drive shaft

123 Eccentric bore

125 Eccentric bearing

128 Inner race

129 Female-threaded portion

130 Outer race

131 Eccentric peg

132 Screw bolt

150 Sanding plate

212 Housing

220 Motor

221 Threaded portion

222 Drive shaft

230 Outer race

232 Sealing means

241 Bearing

242 Bearing

425 Eccentric bearing

501 Sanding pad holder

502 Bearing eye

503 Sanding pad

541 Ventilator

542 Extractor muff

544 Suction hole

What is claimed is:
 1. A power tool (10) with a housing (12, 112, 212)and a motor (20, 120, 220), supported in the housing, that has arotatable drive shaft (22, 122, 222) which is connected operatively byone end to a tool (50, 150), wherein said drive shaft carries a sandingplate that can be equipped with grinding means (52), relative to whichsanding plate the drive shaft (22, 122, 222) is rotatably supported bymeans of a roller bearing with an inner race (28) and outer race (30)spaced apart by a bearing gap (26) and with rotationally fixed androtatably disposed parts, and is provided with means for removinggrinding dust, characterized in that a bearing (425) closely adjacent toany incident grinding dust or chips created has, on at least one side ofits bearing gap (26), two sealing disks (38, 40) disposed side by side,wherein one of D, the two sealing disks (38, 40) disposed on one side isa non-grinding sealing disk relative to the inner race (28) of thebearing (425), and the other is a grinding sealing disk, wherein saidgrinding sealing disk (40) is disposed on the outside of the bearing(425), and the non-grinding sealing disk (38) is disposed on the insideof it, oriented toward the roller bodies.
 2. The power tool (10) ofclaim 1, wherein the two sealing disks (38, 40) are disposed adjacentone another as close together as possible, whereby said disks arebracing one another axially.
 3. The power tool (10) of claim 1, whereinthe sealing disks (38, 40) are disposed in a manner fixed againstrelative rotation by their outer edge (34), on the bearing (425) on itsouter race (30) that is disposed structurally connected to the housingand being capable of snapping into two parallel inner race grooves insaid outer race (36).
 4. The power tool (10) of claim 1, wherein thebearing (425) next to the tool (50, 150) is a roller bearing, which onboth sides of a bearing gap (26) has two sealing disks (38, 40) disposedside by side.
 5. The power tool (10) of claim 1, wherein the bearing(425) is a two-row angular ball bearing.
 6. The power tool (10) of claim1, wherein the two sealing disks (38, 40) rest axially with their outeredge (34), in their mounted position, on the two parallel outer racegrooves (36), and their remaining axial spacing from one another isdictated by a concave profile of said disks toward the balls (31).
 7. Apower tool (10) with a housing (12, 112, 212) and a motor (20, 120,220), supported in the housing, that has a rotatable drive shaft (22,122, 222) which is connected operatively by one end to a tool (50, 150),wherein said drive shaft carries a sanding plate that can be equippedwith grinding means (52), relative to which sanding plate the driveshaft (22, 122, 222) is rotatably supported by means of a roller bearingwith an inner race (28) and outer race (30) spaced apart by a bearinggap (26) and with rotationally fixed and rotatably disposed parts, andis provided with means for removing grinding dust, characterized in thata bearing (425) closely adjacent to any incident grinding dust or chipscreated has, on at least one side of its bearing gap (26), two sealingdisks (38, 40) disposed side by side, wherein the sealing disks (38, 40)comprise plastic, said plastic selected from the group consisting ofRSR, RSL, RST, RSF, and Viton, and wherein said sealing disks (38, 40)include a metal part (44), said metal part (44) comprising zinc-coatedsteel.
 8. A power tool (10) with a housing (12, 112, 212) and a motor(20, 120, 220), supported in the housing, that has a rotatable driveshaft (22, 122, 222) which is connected operatively by one end to a tool(50 150), wherein said drive shaft carries a sanding plate that can beequipped with grinding means (52), relative to which sanding plate thedrive shaft (22, 122, 222) is rotatably supported by means of a rollerbearing with an inner race (28) and outer race (30) spaced apart by abearing gap (26) and with rotationally fixed and rotatably disposedparts, and is provided with means for removing grinding dust,characterized in that a bearing (425) closely adjacent to any incidentgrinding dust or chips created has, on at least one side of its bearinggap (26), two sealing disks (38, 40) disposed side by side, wherein theinner race (28) and the outer race (30) are each approximately 4 mmwider than the inner race and outer race, respectively, of a deep grooveball bearing without sealing disks (38, 40).
 9. A power tool (10) with ahousing (12, 112, 212) and a motor (20, 120, 220), supported in thehousing, that has a rotatable drive shaft (22, 122, 222) which isconnected operatively by one end to a tool (50, 150), wherein said driveshaft carries a sanding plate that can be equipped with grinding means(52), relative to which sanding plate the drive shaft (22, 122, 222) isrotatably supported by means of a roller bearing with an inner race (28)and outer race (30) spaced apart by a bearing gap (26) and withrotationally fixed and rotatably disposed parts, and is provided withmeans for removing grinding dust, characterized in that a bearing (425)closely adjacent to any incident grinding dust or chips created has, onat least one side of its bearing gap (26), two sealing disks (38, 40)disposed side by side, wherein a degree of filling of the bearing (415)with lubricant is between 40% and 50%.